1. The Field of the Invention:
This invention relates to apparatus used to monitor intracompartmental pressures within a body. More particularly, the present invention is directed to an apparatus for use in direct continuous measurement and monitoring of intrauterine pressure during labor and childbirth.
2. The Prior Art:
Each year, approximately 3.5 million children are born within the United States. In order to assist physicians in treating a mother and child approaching childbirth, monitoring devices are commonly used during the final stages of labor to monitor the mother's uterine contractions. Such monitoring devices can quickly provide the physician with information about the rate, duration, and intensity of the mother's uterine contractions and, when a fetal heart monitor is used, the effect of the contractions on the fetal heart rate. This information can help the physician ensure that oxygen and nutrients are being properly transferred from the mother to the fetus during labor and childbirth and can help the physician identify potential problems before they become life-threatening.
It is often the case that uterine contractions are monitored using devices which can be secured externally to the surface of the mother's abdomen. For example, a pressure sensitive button called a tocotransducer is often secured to the mother's abdomen to provide information about the frequency and duration of the uterine contractions.
In many cases, externally secured monitoring devices can provide sufficient information to enable a physician to treat the mother and child during labor and childbirth. It will be appreciated, however, that the use of external monitoring devices may give rise to large measurement errors in some cases due to extraneous noise and/or movement by the mother. In many labor and birthing situations, and particularly where there is a significant risk of complications, a physician may wish to have more accurate measurements than can be obtained using external monitoring devices.
In order to obtain more reliable and accurate information about the mother's uterine contractions, a physician will often initiate intrauterine pressure monitoring. In addition to providing information about the rate and duration of the uterine contractions, intrauterine pressure monitoring can also provide accurate information about the intensity of the uterine contractions. Importantly, since the uterine pressure is being measured directly, errors in measurement due to extraneous noise and movement by the mother are less likely than with external monitoring devices.
One of the most widely used techniques for intrauterine pressure measurement and monitoring uses a liquid-filled catheter inserted into the uterus and then connected externally to a pressure transducer. In using this technique, a rigid guide tube is inserted just inside the mother's cervix. A catheter is then threaded through the guide tube until it extends into the uterus approximately 15 to 20 centimeters (cm). This catheter is filled with a sterile liquid solution, such as, for example, a sterile saline solution. Once the catheter is in place, the guide tube is removed from the cervix and slid away from the mother along the catheter.
After the in-dwelling catheter is positioned as described above, the other end of the catheter is hydraulically coupled to a pressure transducer typically mounted to a bedside IV stand or pole. The pressure transducer is often used with a disposable dome that fits over the tranducer diaphragm. The dome has two ports, one on the side and one vertical. The side port is connected to the in-dwelling liquid-filled catheter after it is primed with sterile solution. The other port is generally used for zero balancing and calibration. The pressure transducer is connected to a monitor device near the patient. Typical monitor devices include cathode ray tube display devices, digital display and/or recording devices, printers, and plotters.
In addition to the proper set-up of the measurement equipment in the above-described manner, when using a liquid-filled catheter, it has been conventional practice to prime the catheter with a sterile solution so that any air bubbles within the catheter are removed and a continuous liquid column is provided from the pressure transducer to the tip of the catheter within the uterus. Then, when the mother's uterus contracts, the increased intrauterine pressure displaces the liquid within the catheter, and the pressure transducer thereby detects a change in the intrauterine pressure. The pressure transducer generates electrical signals proportional to the detected intrauterine pressure, and such signals are then amplified and displayed by the monitor device. Usually, the monitor device is used to display the mother's intrauterine pressure as a function of time, often along with the fetal heart rate, and this data can then be used by the physician and other medical personnel to appropriately diagnose and treat the mother and child.
While the foregoing technique for monitoring intrauterine pressure is widely used and under proper circumstances can produce reliable measurements, there are a number of disadvantages associated with the technique.
One disadvantage of the above-described technique is the time required to fill and prime the catheter with the sterile solution. Particularly in a critical situation, this procedure uses up valuable time, and is somewhat cumbersome since the transducer is connected by a relatively long length of liquid-filled tubing running from the mother over to the bedside pole-mounted transducer. Furthermore, sometimes an air bubble will enter the open end of the catheter. In such cases, it has been the common practice to flush the catheter with sterile solution to remove the air bubble. Occasionally the catheter is replaced altogether under such circumstances.